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Area Forecast Discussion (AFD)

Issued by Caribou, ME (CAR)

FXUS61 KCAR 172249

Area Forecast Discussion
National Weather Service Caribou ME
649 PM EDT Fri May 17 2019

A small area of low pressure will cross the region tonight. 
Weak high pressure will build over the area Saturday and slide 
east Saturday night. A warm front will lift north into the the 
area Sunday.

645pm update...Forecast still looks to be on track for rain
overspreading the area as the low develops in the Gulf of Maine
and the upper trough approaches from Quebec. Did add areas of
fog with the moisture advection. The fog is currently developing
in the Penobscot Bay region as well as the high terrain in
Piscataquis County and will tend to become more widespread
tonight until winds pick up on the backside of the low later

Previous discussion...
An upper level trough is approaching from the NW this afternoon,
easily evident in water vapor satellite. Expect a weak surface
low to develop just ahead of the upper level low this evening
and cross central Maine. The more significant rain tonight will
be north of the low in Northern Maine with a deformation zone,
where one quarter to one half inch is expected. Downeast,
a round of showers is expected this evening just ahead of the
low, with a tenth to a quarter of an inch. There is some
instability, but probably not enough for lightning. Rain tapers
off overnight Downeast, but persists in the north. The steadier
rain in the north will be ending around dawn Saturday. However,
unstable NW flow will allow for mostly cloudy skies and isolated
to scattered light showers mainly in the north through the day 
Saturday, much like what was seen yesterday. Somewhat cool with 
mid 50s north and around 60 Downeast.

Cloudy stretch looks to continue into Sunday. Aloft, upper low
exits into Canadian Maritimes Saturday night into Sunday
morning. The upper ridge that had been locked across the central
US will begin to crest Sunday afternoon over the Northeast, with
a surface warm front approaching from west with rain. Onset
timing continues a slight trend later. The aforementioned jet
streak shows a little weakening, slowing transport into the
region. Greatest QPF will be over the north and central areas
with best overrunning lift. Some showers are still expected
Downeast, but overall lighter precip initially. With the warm
front north of Maine, much of the state will remain in an area 
of warm air advection overnight through Monday. This makes 
Sunday night some 5-10 degrees warmer than Saturday night. Just 
how progressive this front is will determine highs on Monday 
which, across guidance, has the highest variance for the week 
for both Caribou and Bangor. Trailing cold front will pass 
Monday afternoon, with the chance of some thunder across central
Maine. Thunder potential will be maximized if daytime heating 
can increase temps to take advantage of frontal lift and 
maximize lapse rates.

Low pressure begins to move out of area Monday night and
Tuesday. Some lingering showers are anticipated on the back side
of the low during the day. This is again due to NW flow and
diurnal heating. Temperatures begin to rebound mid-week as 
ridging builds. Wednesday and Thursday remain mostly dry, with 
only a slight chance of some showers Thursday. As the ridge 
begins to break down, the chance of rain increases on Friday.

NEAR TERM: Rain and low clouds tonight with IFR to low MVFR
conditions. Improvement to low VFR by mid-morning Downeast, and
to VFR by early afternoon in the north, as the flow becomes
offshore and gradual drying begins.

SHORT TERM: Low clouds will begin to enter region late Saturday
night, dropping conditions to MVFR and then IFR with stratiform
rain across the north. Downeast will see a similar start, but
transition to mostly rain showers through Monday. Much of the
northern sites will remain MVFR through Tuesday night and
Wednesday morning. VFR conditions will return Wednesday

NEAR TERM: Conditions with tonight's weak system should stay
just below small craft, with seas to 4 feet and 10 to 15 knot
winds. Similar conditions continuing into Saturday.

SHORT TERM: Seas begin below SCA Sunday, but will begin to
increase Sunday night. SCA for hazardous seas may be needed
Monday through Monday night. Otherwise, a few wind gusts Tuesday
night could reach SCA criteria of 25kts.


Near Term...Foisy
Short Term...Cornwell
Long Term...Cornwell